Chlorinated hydrocarbons are important as feedstocks or intermediates for the manufacture of various products such as agricultural chemicals, medicinal chemicals and freon alternate materials. For example, trichloroallyl diisopropylthiocarbamate which is useful as a herbicide can be manufactured from 1,1,1,2,3-pentachloropropane through 1,1,2,3-tetracloropropene. The chlorinated hydrocarbons which are feedstocks or intermediates for agricultural and medicinal chemicals must have extremely high purity.
As the process of making such chlorinated hydrocarbons, there is known a three-stage reaction consisting of a first reaction for obtaining a chlorinated saturated hydrocarbon having 3 carbon atoms by adding carbon tetrachloride to an unsaturated compound having 2 carbon atoms, a second reaction for obtaining a chlorinated unsaturated hydrocarbon having 3 carbon atoms by dehydrochlorinating the chlorinated saturated hydrocarbon, and a third reaction for obtaining a chlorinated saturated hydrocarbon having 3 carbon atoms by further adding chlorine to the chlorinated unsaturated hydrocarbon. For example, JP-B 2-47969 discloses a process comprising the steps of carrying out an addition reaction between ethylene and carbon tetrachloride in the presence of a phase transfer catalyst comprising metallic iron and a phosphoryl compound to obtain 1,1,1,3-tetrachloropropane (first reaction), treating this in a sodium hydroxide aqueous solution in the presence of a quaternary ammonium salt or a quaternary phosphonium salt at a temperature of 40 to 80° C. to dehydrochlorinate it so as to obtain a trichloropropene mixture of 1,1,3-trichloropropene and 3,3,3-trichloropropene (second reaction), and applying ultraviolet light to the trichloropropene mixture in the presence of chlorine to chlorinate it so as to obtain 1,1,1,2,3-pentachloropropane (third reaction).
A person skilled in the art can obtain a chlorinated saturated or unsaturated hydrocarbon having desired numbers of carbon atoms and chlorine atoms by selecting an appropriate feedstock compound and carrying out part or all of the above three-stage reaction.
However, the above prior art process of making a chlorinated hydrocarbon has the following problems to be solved in each stage.
In the first reaction, although the iron-phosphoryl compound catalyst in use shows high reactivity right after it is prepared, its activity sharply drops with the passage of time. Therefore, to obtain a desired high degree of conversion, a large amount of the catalyst must be used. However, when a large amount of the catalyst is used, it is difficult to control the reaction due to a sharp rise in reactivity in the initial stage of the reaction, whereby the reaction yield of an object of interest may be impaired. Also when a large amount of the catalyst is used, it takes lots of labor and cost to dispose of the waste catalyst, thereby impeding the curtailment of production cost. Further, the surface of the metallic iron used in the preparation of the iron-phosphoryl compound catalyst is gradually oxidized during its storage, and the initial reaction rate is greatly changed by its oxidized state.
In the second reaction, there is a problem with the cost of sodium hydroxide which is consumed in considerable quantity, and also it takes a lot of labor to dispose of the organic chlorine compound which is dissolved in a water phase to be discarded.
In the optical chlorination reaction which is the third reaction, the reaction time (residence time) must be prolonged to achieve a sufficiently high degree of reaction conversion.
Further, to obtain 1,1,1,2,3-pentachloropropane having high purity as a chlorinated hydrocarbon, the distillation purification of the obtained product is generally carried out after the third reaction. However, when this chlorinated hydrocarbon having a large number of chlorine atoms is purified by distillation, it is very difficult to separate impurities from the chlorinated hydrocarbon. Therefore, an extremely high-performance distillation column is required to obtain a high-purity product, and it takes a long time to carry out precision distillation, thereby causing a cost problem.
As described above, in the three-stage reaction for the manufacture of a chlorinated hydrocarbon, it is desired that an addition reaction should be carried out efficiently at a stable reaction rate to obtain an object of interest at a high degree of conversion while the amount of the catalyst is reduced in the first reaction; a dehydrochlorination reaction should be carried out in such a manner that the production of a by-product to be disposed of is suppressed without using an expensive alkali source in the second reaction; and a chlorination reaction having higher efficiency should be carried out in the third reaction.